
/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>


typedef struct
{
    size_t sbrk_size;
} ngx_http_degradation_main_conf_t;


typedef struct
{
    ngx_uint_t degrade;
} ngx_http_degradation_loc_conf_t;


static ngx_conf_enum_t ngx_http_degrade[] = {
    {ngx_string("204"), 204}, {ngx_string("444"), 444}, {ngx_null_string, 0}};


static void *ngx_http_degradation_create_main_conf(ngx_conf_t *cf);
static void *ngx_http_degradation_create_loc_conf(ngx_conf_t *cf);
static char *ngx_http_degradation_merge_loc_conf(ngx_conf_t *cf, void *parent,
                                                 void *child);
static char *ngx_http_degradation(ngx_conf_t *cf, ngx_command_t *cmd,
                                  void *conf);
static ngx_int_t ngx_http_degradation_init(ngx_conf_t *cf);


static ngx_command_t ngx_http_degradation_commands[] = {

    {ngx_string("degradation"), NGX_HTTP_MAIN_CONF | NGX_CONF_TAKE1,
     ngx_http_degradation, NGX_HTTP_MAIN_CONF_OFFSET, 0, NULL},

    {ngx_string("degrade"),
     NGX_HTTP_MAIN_CONF | NGX_HTTP_SRV_CONF | NGX_HTTP_LOC_CONF
         | NGX_CONF_TAKE1,
     ngx_conf_set_enum_slot, NGX_HTTP_LOC_CONF_OFFSET,
     offsetof(ngx_http_degradation_loc_conf_t, degrade), &ngx_http_degrade},

    ngx_null_command};


static ngx_http_module_t ngx_http_degradation_module_ctx = {
    NULL,                      /* preconfiguration */
    ngx_http_degradation_init, /* postconfiguration */

    ngx_http_degradation_create_main_conf, /* create main configuration */
    NULL,                                  /* init main configuration */

    NULL, /* create server configuration */
    NULL, /* merge server configuration */

    ngx_http_degradation_create_loc_conf, /* create location configuration */
    ngx_http_degradation_merge_loc_conf   /* merge location configuration */
};


ngx_module_t ngx_http_degradation_module = {
    NGX_MODULE_V1,
    &ngx_http_degradation_module_ctx, /* module context */
    ngx_http_degradation_commands,    /* module directives */
    NGX_HTTP_MODULE,                  /* module type */
    NULL,                             /* init master */
    NULL,                             /* init module */
    NULL,                             /* init process */
    NULL,                             /* init thread */
    NULL,                             /* exit thread */
    NULL,                             /* exit process */
    NULL,                             /* exit master */
    NGX_MODULE_V1_PADDING};


static ngx_int_t
ngx_http_degradation_handler(ngx_http_request_t *r)
{
    ngx_http_degradation_loc_conf_t *dlcf;

    dlcf = ngx_http_get_module_loc_conf(r, ngx_http_degradation_module);

    if (dlcf->degrade && ngx_http_degraded(r))
    {
        return dlcf->degrade;
    }

    return NGX_DECLINED;
}


ngx_uint_t
ngx_http_degraded(ngx_http_request_t *r)
{
    time_t                            now;
    ngx_uint_t                        log;
    static size_t                     sbrk_size;
    static time_t                     sbrk_time;
    ngx_http_degradation_main_conf_t *dmcf;

    dmcf = ngx_http_get_module_main_conf(r, ngx_http_degradation_module);

    if (dmcf->sbrk_size)
    {
        log = 0;
        now = ngx_time();

        /* lock mutex */

        if (now != sbrk_time)
        {
            /*
             * ELF/i386 is loaded at 0x08000000, 128M
             * ELF/amd64 is loaded at 0x00400000, 4M
             *
             * use a function address to subtract the loading address
             */

            sbrk_size = (size_t)sbrk(0) - ((uintptr_t)ngx_palloc & ~0x3FFFFF);
            sbrk_time = now;
            log       = 1;
        }

        /* unlock mutex */

        if (sbrk_size >= dmcf->sbrk_size)
        {
            if (log)
            {
                ngx_log_error(NGX_LOG_NOTICE, r->connection->log, 0,
                              "degradation sbrk:%uzM",
                              sbrk_size / (1024 * 1024));
            }

            return 1;
        }
    }

    return 0;
}


static void *
ngx_http_degradation_create_main_conf(ngx_conf_t *cf)
{
    ngx_http_degradation_main_conf_t *dmcf;

    dmcf = ngx_pcalloc(cf->pool, sizeof(ngx_http_degradation_main_conf_t));
    if (dmcf == NULL)
    {
        return NULL;
    }

    return dmcf;
}


static void *
ngx_http_degradation_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_degradation_loc_conf_t *conf;

    conf = ngx_palloc(cf->pool, sizeof(ngx_http_degradation_loc_conf_t));
    if (conf == NULL)
    {
        return NULL;
    }

    conf->degrade = NGX_CONF_UNSET_UINT;

    return conf;
}


static char *
ngx_http_degradation_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_http_degradation_loc_conf_t *prev = parent;
    ngx_http_degradation_loc_conf_t *conf = child;

    ngx_conf_merge_uint_value(conf->degrade, prev->degrade, 0);

    return NGX_CONF_OK;
}


static char *
ngx_http_degradation(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_degradation_main_conf_t *dmcf = conf;

    ngx_str_t *value, s;

    value = cf->args->elts;

    if (ngx_strncmp(value[1].data, "sbrk=", 5) == 0)
    {
        s.len  = value[1].len - 5;
        s.data = value[1].data + 5;

        dmcf->sbrk_size = ngx_parse_size(&s);
        if (dmcf->sbrk_size == (size_t)NGX_ERROR)
        {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "invalid sbrk size \"%V\"",
                               &value[1]);
            return NGX_CONF_ERROR;
        }

        return NGX_CONF_OK;
    }

    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "invalid parameter \"%V\"",
                       &value[1]);

    return NGX_CONF_ERROR;
}


static ngx_int_t
ngx_http_degradation_init(ngx_conf_t *cf)
{
    ngx_http_handler_pt       *h;
    ngx_http_core_main_conf_t *cmcf;

    cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);

    h = ngx_array_push(&cmcf->phases[NGX_HTTP_PREACCESS_PHASE].handlers);
    if (h == NULL)
    {
        return NGX_ERROR;
    }

    *h = ngx_http_degradation_handler;

    return NGX_OK;
}
